WO1996014266A1 - Process for preparing aerogels - Google Patents

Process for preparing aerogels Download PDF

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Publication number
WO1996014266A1
WO1996014266A1 PCT/EP1995/004141 EP9504141W WO9614266A1 WO 1996014266 A1 WO1996014266 A1 WO 1996014266A1 EP 9504141 W EP9504141 W EP 9504141W WO 9614266 A1 WO9614266 A1 WO 9614266A1
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WIPO (PCT)
Prior art keywords
gel
solution
aged
water
sio
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PCT/EP1995/004141
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German (de)
French (fr)
Inventor
Rolf-Michael Jansen
Andreas Zimmermann
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Hoechst Aktiengesellschaft
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Application filed by Hoechst Aktiengesellschaft filed Critical Hoechst Aktiengesellschaft
Priority to US08/836,184 priority Critical patent/US5759506A/en
Priority to JP51499096A priority patent/JP3951307B2/en
Priority to EP95937818A priority patent/EP0789667B1/en
Priority to DE59505981T priority patent/DE59505981D1/en
Publication of WO1996014266A1 publication Critical patent/WO1996014266A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/152—Preparation of hydrogels
    • C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/152—Preparation of hydrogels
    • C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
    • C01B33/1543—Preparation of hydrogels by acidic treatment of aqueous silicate solutions using ion exchangers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/16—Preparation of silica xerogels
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B30/00—Compositions for artificial stone, not containing binders

Definitions

  • the invention relates to a process for the production of modified SiO 2 gels, hereinafter referred to as "aerogels”.
  • Aerogels in the wider sense i.e. in the sense of "gel with air as a dispersing agent" are produced by drying a suitable gel.
  • airgel in this sense includes aerogels in the narrower sense, xerogels and kr ⁇ ogels.
  • a dried gel is referred to as an airgel in the narrower sense if the liquid of the gel is removed at temperatures above the critical temperature and starting from pressures above the critical pressure. If, on the other hand, the liquid of the gel is removed subcritically, for example with the formation of a liquid-vapor boundary phase, the resulting gel is referred to as a xerogel.
  • the gels produced according to the invention are aerogels, in the sense of gel with air as a dispersing agent. Since these gels are produced by subcritical drying, they can also be called xerogels.
  • SiO 2 aerogels are known to have an excellent thermal insulation effect. They can be produced, for example, by acid hydrolysis of tetraethyl orthosilicate in ethanol.
  • the hydrolysis produces a gel, the structure of which can be influenced by the temperature, the pH and the duration of the gelling process.
  • the gel structure generally collapses when the wet gels dry, since the capillary forces that occur during the drying are extremely large.
  • the gel collapse can be prevented by carrying out the drying above the critical temperature and the critical pressure of the solvent. Since the liquid / gaseous phase boundary disappears in this area, the capillary forces are also eliminated and the gel does not change during drying, ie there is no shrinking of the gel during drying.
  • WO 92/20623 discloses a process in which SiO 2 aerogels are produced by hydrolysis and polycondensation of tetraalkoxysilanes, which is characterized in that the alcohol-aqueous gel has been aged in a solution of tetraalkoxysilanes in order to increase the gel network strength.
  • a disadvantage of the prior art is that extremely expensive raw materials such as tetraalkoxysilanes are used both for the production of the gels and for gelation, and that the service life required for aging and network reinforcement is very long.
  • deionized SiO 2 gels which are produced from cheap water glass, can be dried under subcritical conditions if they are aged before drying in an aqueous organic solution of alkyl and / or aryl orthosilicate or free silica leaves.
  • the products obtained are referred to below as "aerogels”. They have an excellent thermal insulation effect.
  • the invention relates to a process for the production of aerogels, which is characterized in that
  • step a) bringing an aqueous water glass solution to a pH value of ⁇ 3 using an acidic ion exchanger or a mineral acid, b) the silica formed is polycondensed by adding a base to an SiO 2 gel and, if a mineral acid was used in step a), the gel is washed with water without electrolyte,
  • step b) optionally washing the gel obtained in step b) with a suitable alcohol or organic solvent until the water content of the gel is ⁇ 20% by weight,
  • a condensation-capable alkyl and / or aryl orthosilicate of formula R 1. 4 n Si (OR 2 ) n , where n 1 to 4 and R 1 and R 2 are, independently of one another, C 1 -C 6 -alkyl, cyclohexyl or phenyl, or can be aged with an aqueous silicic acid solution,
  • step d) the aged gel obtained in step d) dries subcritically.
  • an acidic ion exchange resin is preferably used, in particular those which contain sulfonic acid groups are suitable. If mineral acids are used, hydrochloric acid and sulfuric acid are particularly suitable. Sodium and / or potassium water glass is generally used as the water glass.
  • the base used is preferably NH 4 OH, NaOH, KOH, Al (OH) 3 , colloidal silica and / or water glass.
  • a mineral acid is used in step a)
  • the SiO 2 gel produced with the aid of the base is washed free of electrolytes with water; washing is preferably carried out until the washing water running off has the same electrical conductivity as demineralized water.
  • the gel is preferably allowed to age, generally at a temperature between the freezing point and the boiling point of the solution, preferably at 0 to 120 ° C., particularly preferably at 60 to 100 ° C. and a pH of 4 to 1 1, preferably 4 to 9.
  • the duration of the aging is generally 10 seconds to 48 hours, preferably 10 seconds to 5 hours.
  • the gel in step c) is preferably washed with a suitable alcohol or organic solvent until the water content is ⁇ 10% by weight if the gel enhancement in step d) is carried out with a solution of an alkyl and / or aryl orthosilicate.
  • a suitable alcohol or organic solvent preferably methanol, ethanol, propanol, isopropanol, butanol or isobutanol, are generally used as alcohols. It is also possible to use other organic solvents that are miscible with water, e.g. THF and acetone, as well as mixtures of these solvents.
  • step c) water is preferably used as the solvent if the gel enhancement in step d) is carried out with an inorganic, low molecular weight silica. It may be advantageous to add organic admixtures (alcohols, aldehydes and / or ketones) to the aqueous phase as part of a solvent exchange, and to vary the pH between 3 and 11 in order to determine the rate of condensation and the deposition of SiO 2 to influence the silica added in step d).
  • organic admixtures alcohols, aldehydes and / or ketones
  • the gel reinforcement carried out in step d) is carried out by introducing (for example diffusion) an SiO 2 source capable of condensation into the pore volume of the gel produced in step b) and optionally prepared in step c) and then depositing the SiO 2 source on the existing one Gel framework through condensation reaction.
  • the SiO 2 source is either an alkyl and / or aryl orthosilicate of the formula R 1 4 _ n Si (OR 2 ) n , or a dilute solution of a low molecular weight silica used.
  • the gel prepared in step c) is aged in an alcoholic solution of the orthosilicate.
  • the concentration of the orthosilicate in the alcoholic solution is 0.1 to 30% by volume, preferably 1 to 10% by volume.
  • Linear or branched aliphatic alcohols preferably methanol, ethanol, propanol, isopropanol, butanol or isobutanol, are generally used as alcohols.
  • the duration of the aging is generally 10 minutes to 48 hours, preferably 10 minutes to 24 hours.
  • silica solution with a concentration of 1 to 10% by weight, particularly preferably 4 to 7% by weight, which was prepared, for example, by exchanging the cations on a previously described ion exchange resin.
  • organic fractions such as ketones, aldehydes and branched and unbranched alcohols can be added to the solution in a suitable concentration in order to ensure the polycondensation of the silica, the cluster growth of the polycondensates that form and the deposition on the one formed in step b) and optionally in section c) to influence the prepared gel framework.
  • the upper limit of the total organic admixture depends on the precipitation of the first SiO components.
  • Steps a) to d) are preferably carried out at a temperature between the freezing point of the solution and 150 ° C. and a pressure of 1 to 10 bar.
  • the aged gel is dried subcritically, preferably at temperatures from -30 to 200 ° C., particularly preferably from 0 to 150 ° C.
  • the pressures used in the drying are preferably 0.001 to 20 bar, particularly preferably 0.01 to 5 bar. Drying is generally continued until the gel has a residual solvent content of less than 0.1% by weight.
  • 1 l of a sodium water glass solution (with a content of 8% by weight SiO 2 and a Na O: SiO 2 ratio of 1: 3.3) is passed through a column (diameter: 50 mm, length: 300 mm) (20 ml / min), the acidic ion exchange resin of a (styrene-divinylbenzene copolymer having sulfonic acid groups, is commercially available under the name Duolite ® filled C20) with 0.5 I.
  • the pH of the flowing solution is 2.3.
  • the solution is then adjusted to a pH of 5.6 with 1 molar NaOH solution.
  • the resulting gel is then mechanically comminuted with an agitator (average particle size ⁇ 0.5 mm) and then the water is removed from the gel with ethanol at 50 ° C. in a continuously operating extraction vessel until the residual water content in the gel is ⁇ 10% by weight is.
  • the gel is then aged at 60 ° C. for 24 hours in an ethanolic tetraethyl orthosilicate solution (concentration 10% by volume).
  • the gel is dried in a nitrogen-purged dryer (6 hours at 60 ° C and 12 hours at 150 ° C).
  • the transparent airgel thus obtained has a density of 0.25 g / cm 3 .
  • the BET specific surface area is about 820 m 2 / g.
  • the ⁇ value is 0.027 W / mK.
  • the thermal conductivity was measured using a heating wire method (see e.g. O. Nielsson, G. Joschenpöhler, J. subject, J. Fricke, High Temperatures-High Pressures, Vol. 21, 267-274 (1989)).

Abstract

The invention concerns a process for preparing modified SiO2 gels, in which the gel is aged with a solution of an alkyl and/or arylorthosilicate capable of condensation or with an aqueous silicic acid solution in order to reinforce the network.

Description

Beschreibung description
Verfahren zur Herstellung von AerogelenProcess for the production of aerogels
Die Erfindung betrifft ein Verfahren zur Herstellung von modifizierten SiO2-Gelen, im folgenden "Aerogele" genannt.The invention relates to a process for the production of modified SiO 2 gels, hereinafter referred to as "aerogels".
Aerogele im weiteren Sinn, d.h. im Sinne von "Gel mit Luft als Dispersionsmittel", werden durch Trocknung eines geeigneten Gels hergestellt. Unter den Begriff "Aerogel" in diesem Sinne, fallen Aerogele im engeren Sinne, Xerogele und Krγogele. Dabei wird ein getrocknetes Gel als Aerogel im engeren Sinn bezeichnet, wenn die Flüssigkeit des Gels bei Temperaturen oberhalb der kritischen Temperatur und ausgehend von Drücken oberhalb des kritischen Druckes entfernt wird. Wird die Flüssigkeit des Gels dagegen unterkritisch, beispielsweise unter Bildung einer Flüssig-Dampf-Grenzphase entfernt, dann bezeichnet man das entstandene Gel als Xerogel. Es ist anzumerken, daß es sich bei den erfindungsgemäß hergestellten Gelen um Aerogele, im Sinne von Gel mit Luft als Dispersionsmittel handelt. Da diese Gele durch unterkritische Trocknung hergestellt werden, können sie aber auch als Xerogele bezeichnet werden.Aerogels in the wider sense, i.e. in the sense of "gel with air as a dispersing agent" are produced by drying a suitable gel. The term "airgel" in this sense includes aerogels in the narrower sense, xerogels and krγogels. A dried gel is referred to as an airgel in the narrower sense if the liquid of the gel is removed at temperatures above the critical temperature and starting from pressures above the critical pressure. If, on the other hand, the liquid of the gel is removed subcritically, for example with the formation of a liquid-vapor boundary phase, the resulting gel is referred to as a xerogel. It should be noted that the gels produced according to the invention are aerogels, in the sense of gel with air as a dispersing agent. Since these gels are produced by subcritical drying, they can also be called xerogels.
SiO2-Aerogele sind dafür bekannt, daß sie eine hervorragende Wärmeisolationswirkung aufweisen. Sie können beispielsweise durch saure Hydrolyse von Tetraethylorthosilikat in Ethanol hergestellt werden. Bei der Hydrolyse entsteht ein Gel, dessen Struktur durch die Temperatur, den pH-Wert und die Dauer des Gelierprozesses beeinflußt werden kann. Jedoch kollabiert die Gelstruktur im allgemeinen bei der Trocknung der nassen Gele, da die bei der Trocknung auftretenden Kapillarkräfte extrem groß sind. Der Gelkollaps kann dadurch verhindert werden, daß die Trocknung oberhalb der kritischen Temperatur und des kritischen Druckes des Lösungsmittels durchgeführt wird. Da in diesem Bereich die Phasengrenze flüssig/gasförmig verschwindet, entfallen auch die Kapillarkräfte und das Gel verändert sich während der Trocknung nicht, d.h. es tritt auch kein Schrumpfen des Gels während der Trocknung auf. Auf dieser Trocknungstechnik basierende Herstellungsverfahren sind z.B. aus der EP-B-0 396 076 oder der WO 92/03378 bekannt. Diese Technik erfordert aber, beispielsweise bei der Verwendung von Ethanol, eine Temperatur über 240 °C und Drücke bis 40 bar. Der Austausch von Ethanol gegen CO2 vor der Trocknung erniedrigt zwar die Trocknungstemperatur auf ca. 40°C, der benötigte Druck liegt dann aber bei 80 bar.SiO 2 aerogels are known to have an excellent thermal insulation effect. They can be produced, for example, by acid hydrolysis of tetraethyl orthosilicate in ethanol. The hydrolysis produces a gel, the structure of which can be influenced by the temperature, the pH and the duration of the gelling process. However, the gel structure generally collapses when the wet gels dry, since the capillary forces that occur during the drying are extremely large. The gel collapse can be prevented by carrying out the drying above the critical temperature and the critical pressure of the solvent. Since the liquid / gaseous phase boundary disappears in this area, the capillary forces are also eliminated and the gel does not change during drying, ie there is no shrinking of the gel during drying. Manufacturing processes based on this drying technique are known, for example, from EP-B-0 396 076 or WO 92/03378. However, this technique requires, for example when using ethanol, a temperature above 240 ° C and pressures up to 40 bar. Replacing ethanol with CO 2 before drying lowers the drying temperature to approx. 40 ° C, but the required pressure is then 80 bar.
In der WO 92/20623 wird ein Verfahren offenbart, bei dem SiO2-Aerogele durch Hydrolyse und Polykondensation von Tetraalkoxysilanen hergestellt werden, das dadurch gekennzeichnet ist, daß das alkohol-wäßrige Gel in einer Lösung Tetraalkoxysilanen gealtert wurde, um die Gelnetzwerkstärke zu erhöhen. Nachteilig zum Stand der Technik ist jedoch, daß sowohl zur Herstellung der Gele als auch zur Gelalterung äußerst teure Rohmaterialien wie Tetraalkoxysilane eingesetzt werden und daß die erforderlichen Standzeiten zur Gelalterung und Netz werkverstärkung sehr lang sind.WO 92/20623 discloses a process in which SiO 2 aerogels are produced by hydrolysis and polycondensation of tetraalkoxysilanes, which is characterized in that the alcohol-aqueous gel has been aged in a solution of tetraalkoxysilanes in order to increase the gel network strength. A disadvantage of the prior art, however, is that extremely expensive raw materials such as tetraalkoxysilanes are used both for the production of the gels and for gelation, and that the service life required for aging and network reinforcement is very long.
Es wurde nun gefunden, daß man entionisierte SiO2-Gele, die aus billigem Wasserglas hergestellt werden, bei unterkritischen Bedingungen trocknen kann, wenn man sie vor der Trocknung in einer wäßrig-organischen Lösung aus Alkyl- und/oder Arylorthosilikat bzw. freier Kieselsäure altern läßt. Die erhaltenen Produkte werden im folgenden als "Aerogele" bezeichnet. Sie weisen eine hervorragende Wärmeisolationswirkung auf.It has now been found that deionized SiO 2 gels, which are produced from cheap water glass, can be dried under subcritical conditions if they are aged before drying in an aqueous organic solution of alkyl and / or aryl orthosilicate or free silica leaves. The products obtained are referred to below as "aerogels". They have an excellent thermal insulation effect.
Gegenstand der Erfindung ist ein Verfahren zur Herstellung von Aerogelen, das dadurch gekennzeichnet ist, daß manThe invention relates to a process for the production of aerogels, which is characterized in that
a) eine wäßrige Wasserglaslösung mit Hilfe eines sauren lonentauschers oder einer Mineralsäure auf einen pH-Wert ≤ 3 bringt, b) die dabei entstandene Kieselsäure durch Zugabe einer Base zu einem SiO2-Gel polykondensiert und, falls in Schritt a) eine Mineralsäure benutzt wurde, das Gel mit Wasser elektrolytfrei wäscht,a) bringing an aqueous water glass solution to a pH value of ≤ 3 using an acidic ion exchanger or a mineral acid, b) the silica formed is polycondensed by adding a base to an SiO 2 gel and, if a mineral acid was used in step a), the gel is washed with water without electrolyte,
c) gegebenenfalls das in Schritt b) erhaltene Gel mit einem geeigneten Alkohol oder organischen Lösungsmittel solange wäscht, bis der Wassergehalt des Gels < 20 Gew.-% ist,c) optionally washing the gel obtained in step b) with a suitable alcohol or organic solvent until the water content of the gel is <20% by weight,
d) das in Schritt b) oder c) erhaltene Gel zur Netzwerkverstärkung mit einer Lösung eines zur Kondensation befähigten Alkyl- und/oder Arylorthosilikates der Formel R1 4.nSi(OR2)n, wobei n = 1 bis 4 ist und R1 und R2 unabhängig voneinander C.,-C6-Alkyl, Cyclohexyl oder Phenyl sind, oder mit einer wäßrigen Kieselsäure-Lösung altern läßt,d) in step b) or c) obtained gel for network reinforcement with a solution of a condensation-capable alkyl and / or aryl orthosilicate of formula R 1. 4 n Si (OR 2 ) n , where n = 1 to 4 and R 1 and R 2 are, independently of one another, C 1 -C 6 -alkyl, cyclohexyl or phenyl, or can be aged with an aqueous silicic acid solution,
e) das ins Schritt d) erhaltene, gealterte Gel unterkritisch trocknet.e) the aged gel obtained in step d) dries subcritically.
In Schritt a) wird vorzugsweise ein saures lonentauscherharz eingesetzt, wobei insbesondere solche geeignet sind, die Sulfonsäuregruppen enthalten. Falls man Mineralsäuren einsetzt, sind vor allem Salzsäure und Schwefelsäure geeignet. Als Wasserglas wird im allgemeinen Natrium- und/oder Kaliumwasserglas verwendet.In step a) an acidic ion exchange resin is preferably used, in particular those which contain sulfonic acid groups are suitable. If mineral acids are used, hydrochloric acid and sulfuric acid are particularly suitable. Sodium and / or potassium water glass is generally used as the water glass.
In Schritt b) wird als Base vorzugsweise NH4OH, NaOH, KOH, AI(OH)3, kolloidale Kieselsäure und/oder Wasserglas eingesetzt. Falls man in Schritt a) eine Mineralsäure verwendet, wird das mit Hilfe der Base erzeugte SiO2-Gel mit Wasser elektrolytfrei gewaschen; vorzugsweise wird dabei solange gewaschen, bis das ablaufende Waschwasser dieselbe elektrische Leitfähigkeit hat wie entmineralisiertes Wasser. Vor Schritt c) läßt man das Gel vorzugsweise altern, und zwar im allgemeinen bei einer Temperatur zwischen dem Gefrierpunkt und dem Siedepunkt der Lösung, vorzugsweise bei 0 bis 120°C, besonders bevorzugt bei 60 bis 100°C und einem pH-Wert von 4 bis 1 1 , vorzugsweise 4 bis 9. Die Dauer der Alterung beträgt im allgemeinen 10 Sekunden bis 48 Stunden, vorzugsweise 10 Sekunden bis 5 Stunden.In step b) the base used is preferably NH 4 OH, NaOH, KOH, Al (OH) 3 , colloidal silica and / or water glass. If a mineral acid is used in step a), the SiO 2 gel produced with the aid of the base is washed free of electrolytes with water; washing is preferably carried out until the washing water running off has the same electrical conductivity as demineralized water. Before step c), the gel is preferably allowed to age, generally at a temperature between the freezing point and the boiling point of the solution, preferably at 0 to 120 ° C., particularly preferably at 60 to 100 ° C. and a pH of 4 to 1 1, preferably 4 to 9. The duration of the aging is generally 10 seconds to 48 hours, preferably 10 seconds to 5 hours.
Vorzugsweise wäscht man das Gel im Schritt c) mit einem geeigneten Alkohol oder organischen Lösungsmittel solange, bis der Wassergehalt < 10 Gew.-% ist, wenn die Gelverstärkung im Schritt d) mit einer Lösung eines Alkyl- und/oder Arylorthosilikates durchgeführt wird. Als Alkohole werden im allgemeinen lineare oder verzweigte aliphatische Alkohole, vorzugsweise Methanol, Ethanol, Propanol, iso-Propanol, Butanol oder iso-Butanol, verwendet. Es ist auch möglich andere organische Lösungsmittel einzusetzen, die mit Wasser mischbar sind, wie z.B. THF und Aceton, sowie Mischungen aus diesen Lösungsmitteln.The gel in step c) is preferably washed with a suitable alcohol or organic solvent until the water content is <10% by weight if the gel enhancement in step d) is carried out with a solution of an alkyl and / or aryl orthosilicate. Linear or branched aliphatic alcohols, preferably methanol, ethanol, propanol, isopropanol, butanol or isobutanol, are generally used as alcohols. It is also possible to use other organic solvents that are miscible with water, e.g. THF and acetone, as well as mixtures of these solvents.
In Schritt c) wird als Lösungsmittel vorzugsweise Wasser verwendet, wenn die Gelverstärkung in Schritt d) mit einer anorganischen, niedermolekularen Kieselsäure durchgeführt wird. Es kann vorteilhaft sein, der wäßrigen Phase im Rahmen eines Lösungsmittel-Tausches organische Beimischungen (Alkohole, Aldehyde und/oder Ketone) zuzusetzen, sowie den pH-Wert zwischen 3 und 1 1 zu variieren, um die Kondensationsgeschwindigkeit und das Abscheiden des SiO2 aus der im Schritt d) zugesetzten Kieselsäure zu beeinflussen.In step c) water is preferably used as the solvent if the gel enhancement in step d) is carried out with an inorganic, low molecular weight silica. It may be advantageous to add organic admixtures (alcohols, aldehydes and / or ketones) to the aqueous phase as part of a solvent exchange, and to vary the pH between 3 and 11 in order to determine the rate of condensation and the deposition of SiO 2 to influence the silica added in step d).
Die in Schritt d) durchgeführte Gelverstärkung erfolgt durch Einbringen (z.B. Diffusion) einer zur Kondensation befähigten SiO2-Quelle in das Porenvolumen des im Schritt b) hergestellten und gegebenenfalls in Schritt c) vorbereiteten Gels und anschließende Abscheidung der SiO2-Quelle auf dem bestehenden Gelgerüst durch Kondensationsreaktion.The gel reinforcement carried out in step d) is carried out by introducing (for example diffusion) an SiO 2 source capable of condensation into the pore volume of the gel produced in step b) and optionally prepared in step c) and then depositing the SiO 2 source on the existing one Gel framework through condensation reaction.
Als SiO2-Quelle wird entweder ein Alkyl und/oder Arylorthosilikat der Formel R1 4_nSi(OR2)n, oder eine verdünnte Lösung einer niedermolekularen Kieselsäure eingesetzt.The SiO 2 source is either an alkyl and / or aryl orthosilicate of the formula R 1 4 _ n Si (OR 2 ) n , or a dilute solution of a low molecular weight silica used.
Soll die Gelverstärkung durch das o.g. Orthosilikat oder Mischungen unterschiedlicher Orthosilikate der gleichen allgemeinen Formel erfolgen, so wird das in Schritt c) vorbereitete Gel in einer alkoholischen Lösung des Orthosilikates gealtert. Ais Orthosilikate werden vorzugsweise Orthosilikate der Formel R1 .nSi(OR2)n mit n = 1 bis 4 eingesetzt, wobei R1 und R2 unabhängig voneinander C^Cg- Alkyl, Cyclohexyl oder Phenyl sind. Besonders bevorzugt verwendet man Tetraethyl- und/oder Tetramethylorthosilikat. Die Konzentration des Orthosilikates in der alkoholischen Lösung beträgt 0, 1 bis 30 Vol.-%, vorzugsweise 1 bis 10 Vol.-%. Als Alkohole werden im allgemeinen lineare oder verzweigte aliphatische Alkohole, vorzugsweise Methanol, Ethanol, Propanol, iso-Propanol, Butanol oder iso-Butanol, verwendet. Die Dauer der Alterung beträgt im allgemeinen 10 Minuten bis 48 Stunden, vorzugsweise 10 Minuten bis 24 Stunden.If the gel is to be reinforced by the above-mentioned orthosilicate or mixtures of different orthosilicates of the same general formula, the gel prepared in step c) is aged in an alcoholic solution of the orthosilicate. Orthosilicates are preferably orthosilicates of the formula R 1 . n Si (OR 2 ) n used with n = 1 to 4, where R 1 and R 2 are independently C 1 -C 6 -alkyl, cyclohexyl or phenyl. Tetraethyl and / or tetramethyl orthosilicate is particularly preferably used. The concentration of the orthosilicate in the alcoholic solution is 0.1 to 30% by volume, preferably 1 to 10% by volume. Linear or branched aliphatic alcohols, preferably methanol, ethanol, propanol, isopropanol, butanol or isobutanol, are generally used as alcohols. The duration of the aging is generally 10 minutes to 48 hours, preferably 10 minutes to 24 hours.
Alternativ zu der Verwendung von Orthosilikaten zur Gelverstärkung in Schritt d) können auch verdünnte, wäßrige Lösungen von niedermolekularer Kieselsäure und/oder Alkalisilikaten eingesetzt werden. Bei Verwendung der freien Kieselsäure, die z.B. über einen zuvor beschriebenen lonenaustausccher aus einer wäßrigen Lösung erhalten werden kann, besteht der Vorteil, daß keine Salzionen aus der pH-Wert Änderung und Neutralisation der Wasserglaslösung im Gel zurückbleiben, die sich negativ auf die Trocknung auswirken. Bevorzugt ist eine Kieselsäure-Lösung mit einer Konzentration von 1 bis 10 Gew.-%, besonders bevorzugt 4 bis 7 Gew.-%, die z.B. durch Austausch der Kationen an einem zuvor beschriebenen lonenaustauscherharz hergestellt wurde. Weiterhin können der Lösung organische Anteile wie z.B. Ketone, Aldehyde sowie verzweigte und unverzweigte Alkohole in geeigneter Konzentration zugesetzt sein, um die Polykondensation der Kieselsäure, das Clusterwachstum der sich bildenden Polykondensate sowie das Abscheiden auf dem in Schritt b) gebildeten und gegebenenfalls im Schnitt c) vorbereiteten Gelgerüsts zu beeinflussen. Die Obergrenze der gesamten organischen Beimischung richtet sich nach dem Ausfällen erster SiO -Anteile. Die Schritte a) bis d) werden vorzugsweise bei einer Temperatur zwischen dem Gefrierpunkt der Lösung und 150°C und einem Druck von 1 bis 10 bar durchgeführt.As an alternative to the use of orthosilicates for gel reinforcement in step d), it is also possible to use dilute, aqueous solutions of low molecular weight silica and / or alkali silicates. When using the free silica, which can be obtained from an aqueous solution, for example via a previously described ion exchanger, there is the advantage that no salt ions remain in the gel from the pH change and neutralization of the water glass solution, which have a negative effect on the drying. Preference is given to a silica solution with a concentration of 1 to 10% by weight, particularly preferably 4 to 7% by weight, which was prepared, for example, by exchanging the cations on a previously described ion exchange resin. Furthermore, organic fractions such as ketones, aldehydes and branched and unbranched alcohols can be added to the solution in a suitable concentration in order to ensure the polycondensation of the silica, the cluster growth of the polycondensates that form and the deposition on the one formed in step b) and optionally in section c) to influence the prepared gel framework. The upper limit of the total organic admixture depends on the precipitation of the first SiO components. Steps a) to d) are preferably carried out at a temperature between the freezing point of the solution and 150 ° C. and a pressure of 1 to 10 bar.
In Schritt e) wird das gealterte Gel unterkritisch, vorzugsweise bei Temperaturen von -30 bis 200°C, besonders bevorzugt von 0 bis 150°C getrocknet. Die bei der Trocknung angewandten Drücke liegen vorzugsweise bei 0,001 bis 20 bar, besonders bevorzugt bei 0,01 bis 5 bar. Die Trocknung wird im allgemeinen solange fortgeführt, bis das Gel einen Lösungsmittel-Restgehalt von weniger als 0,1 Gew.-% aufweist.In step e), the aged gel is dried subcritically, preferably at temperatures from -30 to 200 ° C., particularly preferably from 0 to 150 ° C. The pressures used in the drying are preferably 0.001 to 20 bar, particularly preferably 0.01 to 5 bar. Drying is generally continued until the gel has a residual solvent content of less than 0.1% by weight.
Das erfindungsgemäße Verfahren wird im folgenden an einem Ausführungsbeispiel näher beschrieben.The method according to the invention is described in more detail below using an exemplary embodiment.
Beispielexample
1 I einer Natriumwasserglaslösung (mit einem Gehalt von 8 Gew.-% SiO2 und einem Na O:SiO2 Verhältnis von 1 :3,3) wird über eine Kolonne (Durchmesser: 50 mm, Länge: 300 mm) geleitet (20 ml/min), die mit 0,5 I eines sauren lonentauscherharzes (Styroldivinylbenzolcopolymer mit Sulfonsäuregruppen, handelsüblich unter dem Namen Duolite® C20) gefüllt ist. Der pH-Wert der abfließenden Lösung beträgt 2,3. Anschließend wird die Lösung mit 1 molarer NaOH-Lösung auf einen pH von 5,6 eingestellt. Danach wird das entstandene Gel mechanisch mit einem Rührwerk zerkleinert (mittlere Korngröße < 0,5 mm) und anschließend das Wasser aus dem Gel mit Ethanol bei 50°C in einem kontinuierlich arbeitenden Extraktionsgefäß entfernt, bis der Restwassergehalt im Gel < 10 Gew.-% ist. Danach wird das Gel bei 60°C für 24 Stunden in einer ethanolischen Tetraethylorthosilikat-Lösung (Konzentration 10 Vol.-%) gealtert. Die Trocknung des Gels erfolgt in einem stickstoffgespülten Trockner (6 Stunden bei 60°C und 12 Stunden bei 150°C). Das so erhaltene, transparente Aerogel weist eine Dichte von 0,25 g/cm3 auf. Die spezifische Oberfläche nach BET beträgt etwa 820 m2/g. Der Λ-Wert liegt bei 0,027 W/mK.1 l of a sodium water glass solution (with a content of 8% by weight SiO 2 and a Na O: SiO 2 ratio of 1: 3.3) is passed through a column (diameter: 50 mm, length: 300 mm) (20 ml / min), the acidic ion exchange resin of a (styrene-divinylbenzene copolymer having sulfonic acid groups, is commercially available under the name Duolite ® filled C20) with 0.5 I. The pH of the flowing solution is 2.3. The solution is then adjusted to a pH of 5.6 with 1 molar NaOH solution. The resulting gel is then mechanically comminuted with an agitator (average particle size <0.5 mm) and then the water is removed from the gel with ethanol at 50 ° C. in a continuously operating extraction vessel until the residual water content in the gel is <10% by weight is. The gel is then aged at 60 ° C. for 24 hours in an ethanolic tetraethyl orthosilicate solution (concentration 10% by volume). The gel is dried in a nitrogen-purged dryer (6 hours at 60 ° C and 12 hours at 150 ° C). The transparent airgel thus obtained has a density of 0.25 g / cm 3 . The BET specific surface area is about 820 m 2 / g. The Λ value is 0.027 W / mK.
Die Wärmeleitfähigkeit wurde mit einer Heizdrahtmethode (s. z.B. O. Nielsson, G. Rüschenpöhler, J. Groß, J. Fricke, High Temperatures-High Pressures, Vol. 21 , 267-274 (1989)) gemessen. The thermal conductivity was measured using a heating wire method (see e.g. O. Nielsson, G. Rüschenpöhler, J. Groß, J. Fricke, High Temperatures-High Pressures, Vol. 21, 267-274 (1989)).

Claims

Patentansprüche: Claims:
1. Verfahren zur Herstellung von Aerogelen, dadurch gekennzeichnet, daß man1. A process for the production of aerogels, characterized in that
a) eine wäßrige Wasserglaslösung mit Hilfe eines sauren lonentauschers oder einer Mineralsäure auf einen pH-Wert ≤ 3 bringt,a) bringing an aqueous water glass solution to a pH value of ≤ 3 using an acidic ion exchanger or a mineral acid,
b) die dabei entstandene Kieselsäure durch Zugabe einer Base zu einem SiO2-Gel polykondensiert und, falls in Schritt a) eine Mineralsäure benutzt wurde, das Gel mit Wasser elektrolytfrei wäscht,b) the silica formed is polycondensed by adding a base to an SiO 2 gel and, if a mineral acid was used in step a), the gel is washed with water without electrolyte,
c) gegebenenfalls das in Schritt b) erhaltene Gel mit einem geeigneten Alkohol oder organischen Lösungsmittel solange wäscht, bis der Wassergehalt des Gels < 20 Gew.-% ist,c) optionally washing the gel obtained in step b) with a suitable alcohol or organic solvent until the water content of the gel is <20% by weight,
d) das in Schritt b) oder c) erhaltene Gel zur Netzwerkverstärkung mit einer Lösung eines zur Kondensation befähigten Alkyl- und /oder Arylorthosilikates der Formel R1 4.nSi(OR2)n, wobei n = 1 bis 4 ist und R1 und R2 unabhängig voneinander C1-C6-Alkyl, Cyclohexyl oder Phenyl sind, oder mit einer wäßrigen Kieselsäure-Lösung altern läßt,d) in step b) or c) obtained gel for network reinforcement with a solution of a condensation-capable alkyl and / or aryl orthosilicate of formula R 1. 4 n Si (OR 2 ) n , where n = 1 to 4 and R 1 and R 2 independently of one another are C 1 -C 6 alkyl, cyclohexyl or phenyl, or can be aged with an aqueous silicic acid solution,
e) das in Schritt d) erhaltene, gealterte Gel unterkritisch trocknet.e) the aged gel obtained in step d) dries subcritically.
2. Verfahren gemäß Anspruch 1 , dadurch gekennzeichnet, daß man in Schritt b) als Base NH4OH, NaOH, KOH, AI(OH)3, kolloidale Kieselsäure und/oder Wasserglas einsetzt. 2. The method according to claim 1, characterized in that one uses in step b) as base NH 4 OH, NaOH, KOH, Al (OH) 3 , colloidal silica and / or water glass.
3. Verfahren gemäß Anspruch 1 oder 2, dadurch gekennzeichnet, daß man das in Schritt b) erhaltenen SiO2-Gel bei einer Temperatur zwischen dem Gefrierpunkt und dem Siedepunkt der Lösung und einem pH-Wert von3. The method according to claim 1 or 2, characterized in that the SiO 2 gel obtained in step b) at a temperature between the freezing point and the boiling point of the solution and a pH of
4 bis 1 1 für eine Dauer von 10 Sekunden bis 48 Stunden altern läßt, bevor man in Schritt c) das Wasser entfernt.Allow 4 to 11 for a period of 10 seconds to 48 hours before removing the water in step c).
4. Verfahren gemäß mindestens einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß man in Schritt c) lineare oder verzweigte aliphatische Alkohole verwendet.4. The method according to at least one of claims 1 to 3, characterized in that linear or branched aliphatic alcohols are used in step c).
5. Verfahren gemäß mindestens einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß man als Alkohol in den Schritten c) und/oder d) unabhängig voneinander Methanol, Ethanol, Propanol, iso-Propanol, Butanol oder iso-Butanol verwendet.5. The method according to at least one of claims 1 to 4, characterized in that methanol, ethanol, propanol, iso-propanol, butanol or iso-butanol is used independently of one another as alcohol in steps c) and / or d).
6. Verfahren gemäß mindestens einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß man in Schritt d) Tetramethylorthosilikat und/oder Tetraethylorthosilikat verwendet.6. The method according to at least one of claims 1 to 5, characterized in that tetramethylorthosilicate and / or tetraethylorthosilicate is used in step d).
7. Verfahren gemäß mindestens einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß in Schritt d) die Konzentration des Orthosilikats in der alkoholischen Lösung 0,1 bis 30 Vol.-% beträgt.7. The method according to at least one of claims 1 to 6, characterized in that in step d) the concentration of the orthosilicate in the alcoholic solution is 0.1 to 30 vol .-%.
8. Verfahren gemäß mindestens einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, daß man in Schritt d) das Gel 10 Minuten bis 48 Stunden altern läßt.8. The method according to at least one of claims 1 to 7, characterized in that in step d) the gel is aged for 10 minutes to 48 hours.
9. Verfahren gemäß mindestens einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß man die Schritte a) bis d) bei einer Temperatur zwischen dem Gefrierpunkt der Lösung und 150°C und einem Druck von 1 bis 10 bar durchführt. 9. The method according to at least one of claims 1 to 8, characterized in that steps a) to d) are carried out at a temperature between the freezing point of the solution and 150 ° C and a pressure of 1 to 10 bar.
10. Verfahren gemäß mindestens einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, daß man in Schritt e) das gealterte Gel bei -30 bis 200 °C und 0,001 bis 20 bar trocknet.10. The method according to at least one of claims 1 to 9, characterized in that in step e) the aged gel is dried at -30 to 200 ° C and 0.001 to 20 bar.
1 1. Verwendung eines Aerogels, das nach dem Verfahren gemäß mindestens einem der Ansprüche 1 bis 10 hergestellt wurde, als Wärmeisolationsmaterial. 1 1. Use of an airgel, which was prepared by the method according to at least one of claims 1 to 10, as a heat insulation material.
PCT/EP1995/004141 1994-11-03 1995-10-23 Process for preparing aerogels WO1996014266A1 (en)

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JP51499096A JP3951307B2 (en) 1994-11-03 1995-10-23 Airgel production method
EP95937818A EP0789667B1 (en) 1994-11-03 1995-10-23 Process for preparing aerogels
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EP0864531A1 (en) * 1997-03-05 1998-09-16 Armstrong World Industries, Inc. Wet silica gels for aerogel and xerogel thermal insulation and processes for the wet gels
US5877100A (en) * 1996-09-27 1999-03-02 Cabot Corporation Compositions and insulation bodies having low thermal conductivity
US6129949A (en) * 1995-11-10 2000-10-10 Hoecsht Research & Technology Deutschland Gmbh & Co Kg Process for preparing organically modified aerogels using alcohols, wherein the resultant salts are precipitated
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US6129949A (en) * 1995-11-10 2000-10-10 Hoecsht Research & Technology Deutschland Gmbh & Co Kg Process for preparing organically modified aerogels using alcohols, wherein the resultant salts are precipitated
US5877100A (en) * 1996-09-27 1999-03-02 Cabot Corporation Compositions and insulation bodies having low thermal conductivity
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US6481649B1 (en) 1997-05-02 2002-11-19 Cabot Corporation Method for granulating aerogels
US6620355B1 (en) 1997-05-02 2003-09-16 Cabot Corporation Method for compacting aerogels
US6378229B1 (en) 1997-12-19 2002-04-30 Cabot Corporation Method for the sub-critical drying of lyogels to produce aerogels
US7297718B2 (en) 1998-01-14 2007-11-20 Cabot Corporation Method of producing substantially spherical lyogels in water insoluble silylating agents
WO2009027327A1 (en) * 2007-08-24 2009-03-05 Basf Se Production of metal oxide nanoparticles from alkali metallates in organic solvents

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